Along with the recent explosive growth of the Internet, LANs (Local Area Networks) have been set up in more offices and households. Due in part to improvements in digital wireless communications technologies, there has been a rapidly growing need for a wireless LAN (i.e., a LAN that is set up wirelessly in order to remove the burden of cabling). Furthermore, partly because the wireless LAN can be used in a mobile environment of a mobile terminal as typified by a laptop computer, the wireless LAN is expected to be used in appreciable numbers in the future. A representative technology of the wireless LAN is the IEEE 802.11, which is standardized by the IEEE (Institute of Electrical and Electronics Engineers). This standardized technology defines an OSI (Open System Interconnection) model from a physical layer to an MAC (Media Access Control) layer, which serves as a lower layer of a data link. Further, the IEEE 802.11 can replace the Ethernet (registered trademark), which is a transmission channel in the wired LAN. Furthermore, the IEEE 802.11 is specified to provide a roaming function, which is an optional function peculiar to a wireless method.
Incidentally, a bandwidth of data transmission is reduced when a pair of a transmitter and a receiver communicates with each other by using a specific frequency (a transmission channel) at which another pair of a transmitter and a receiver communicates with each other. In order to avoid this, the devices about to use the transmission channel already occupied by the other devices need to be automatically transferred onto an unused transmission channel.
For example, Patent Document 1 discloses a channel-switching wireless communication device including a wireless communication section. The wireless communication section is provided with a 2.4 GHz band front-end circuit and a 5 GHz band front-end circuit so as to accommodate to the 2.4 GHz and 5 GHz bands. This makes it possible, in a wireless LAN system, to greatly increase the number of transmission channels which can be set simultaneously in the same area. This allows reduction of the risk of an interfering radio wave interrupting a communications link.
Further, Patent Document 2 discloses an information processing system which establishes information communications by searching for an information terminal device capable of the information communications, which determines and collects content which can be processed at a terminal of the information terminal device, and which generates a content information list. This information processing system causes a display section to display at least one of compression format information, bit rate information, sampling rate information, and extension information.
[Patent Document 1]
Japanese Unexamined Patent Publication No. 33676/2002 (Tokukai 2002-33676; published on Jan. 31, 2002) (FIG. 1)
[Patent Document 2]
Japanese Unexamined Patent Publication No. 50589/2003 (Tokukai 2003-50589; published on Feb. 21, 2003) (FIG. 1)
However, in such a conventional wireless communication device, when a communication condition deteriorates, an error rate of data is increased, so that retransmission requests are increased. Therefore, errors cannot be decreased sufficiently within a limited bandwidth, so that irretrievable block noise appears. In such a case, the error rate is reduced by reducing a transmission rate (bit rate), so that the block noise is reduced, but with deterioration in image quality.
The present invention has been made in order to solve the foregoing problems and has as an object to provide a transmitter, a receiver, a wireless system, a control method, a control program, and a computer-readable storage medium storing the same program, all of which make it possible to minimize deterioration of video and audio data and maintain a data transmission rate, as much as possible, even when a communication condition deteriorates.